An updated version of Firefox is available to address the issues with Add-ons disabled or fail to install on Firefox. You can download the update for your OS here: https://www.mozilla.org/firefox/new/
For Known Issues and Workarounds, please check out the update at https://support.mozilla.org/kb/add-ons-disabled-or-fail-to-install-firefox

Explore more topics

Blocking a sender

Thunderbird does not have an option for blocking email messages from specific people or domains. However, you can use message filters to automatically dispose of unwanted messages.

Message filters operate on a per-account basis, so when you set up the filter you must configure it to act on the correct account. The easiest way to do this is:

Select a message from a sender you wish to block: Right-clickPress and hold the Ctrl key, click on the sender's address and choose Create Filter From....

This will open the Filter rules window with the email address already inserted into the filter.

Name the filter. Something like "Block list" would be appropriate.

In the bottom half of the window, change the action to perform to Delete Message.

Click OK to save the filter. The next time that person sends you mail, it will automatically be deleted.

The Message filter that you have created can be opened and edited by selecting the Message filters... entry in the Tools menu. It is not necessary to create an individual filter for each address you want to block.
Now you have the Block list filter, the next time you want to block someone you can add the person's address into the top of the filter by clicking the + button and thus creating a new field to enter the new address. Make sure you select the "Match any of the following" option, as you wish it to fire on any of the listed addresses.